This invention relates to a method of producing multi-layer sliding material.
I have carried out research on multi-layer sliding material and a method of producing same and have developed inventions disclosed in U.S. Pat. No. 4,121,928, U.S. Pat. No. 4,189,522 and Japanese Patent Publication 2441/80. The methods of producing sliding material described in these inventions of prior patents can be summarized as follows. One method is a method of producing multi-layer sliding material in which powder material is supplied to a steel strip and rolled, and the rolled material is then sintered. Another method is a method of producing multi-layer sliding material in which the multi-layer material produced in the first-mentioned method is subjected to rolling and heat treatment, and these process steps can be followed as many times as required.
The powder material used in the aforesaid methods contain aluminum as its main ingredient, and at least one additive selected from the group of low melting point metal lubricants consisting of Pb, Sn, etc., and the group of solid lubricants consisting of metal sulfides, metal-oxides, metal fluorides, etc., the proportion of the additive being 2-40 weight percent. Also, the powder material of the aforesaid composition may, when necessary, be added with at least one aluminum strengthening element selected from the group consisting of Cu, Ni, Si, Mg, and Zn in a proportion of 0.1-15 weight percent in total.
In carrying out the aforesaid methods for producing multi-layer sliding material according to the inventions of prior applications into practice, it has been found that when the rolling step is followed, the surface of the sliding layer (that is, the surface of the alloy layer on the steel strip) of the material tends to develop seizure on the surface of the rolls of the rolling mill.
With an increase in the time required for production, friction between the rolls of the rolling mill and the multi-layer sliding material and heat produced in the material due to plastic deformation thereof cause the temperature of the rolls to rise, and this elevation in temperature is considered responsible for the seizure which makes continuation of production impossible.
The aforesaid rise in temperature in the rolling step has tended to cause the additive contained in the powder material, in particular the low melting point metallic lubricant, to expand in thin yarn form. It has been determined that multi-layer sliding material with a structure of this yarn-like additive distributed therein is low in wear resisting characteristics, and it has been found that laminar peeling tends to occur along the low melting point lubricant additive phase.
An object of this invention is to provide a method of producing multi-layer sliding material which obviates the aforesaid disadvantages of the inventions of the prior applications.
Another object is to provide a method of producing multi-layer sliding material which comprises the step of forced cooling of the powder material, immediately before being subjected to rolling, to a temperature range which is less than 15.degree. C. below room temperature (ambient temperature) whereby seizing of the surface of the alloy layer of the multi-layer sliding material on the roll surface of the rolling mill can be avoided.